Portable heaters are commonly used to provide supplemental heat for a localized area or space to improve the comfort level. There are many heaters having a metal housing such as baseboard, ceramic, parabolic and oil filled heaters. More recently, flame retardant polymers have been used for plastic housings and a fan provides efficient heat transfer. The use of a fan driven motor to provide a forced airflow across the heating elements allows the size of the portable heater to be reduced relative to portable heaters that operate on a natural convection cycle. When the elements are activated the fan motor typically operates at the same speed and does not appreciably vary with heat output. The fan motors are voltage controlled and designed to operate with low current. Typically, the motors are placed in parallel with the heating elements.
Examples of fan driven heaters with at least two different power outputs are disclosed in U.S. Pat. No. 4,755,653, U.S. Pat. No. 5,434,386, U.S. Pat. No. 5,663,633 and U.S. Pat. No. 5,245,691.
Some fan driven portable heaters also include a fan mode where no heat is produced and the device merely operates as a fan. The fan mode typically includes a switch for varying the fan speed. Most portable heaters include two or three heating elements which can be combined to produce three different heat outputs. In most cases, the heating elements are provided in a parallel configuration, however, it is possible to have one of the elements in parallel with two other elements connected in series.
A common heating circuit has the fan motor in parallel with the heating elements and operating with less than 0.5 amps. A switch is provided on the portable heater which allows the user to set the desired heat output level. In the heat generation mode, the fan motor is in parallel with the heating elements, and operates at a constant speed. Portable heaters of this type may include a separate fan speed control which is only operative when the heating elements are not functioning.
Portable heaters are designed to be connected to a 120 volts wall receptacle typically having a 15 amp current capacity. To produce 1500 watts of power this implies the current will be approximately 12.5 amps and produces approximately 5120 BTU's of heat. This amount of heat generation requires a substantial airflow to maintain a low operating temperature with the plastic molded heater housing. A high fan speed is required at the maximum heat output and produces a significant amount of noise. As the fan runs at high speed for all heat output conditions, unnecessary noise is produced at lower heat outputs. Multispeed motors and/or resistors can be used to drop the voltage to the fan motor but significantly add to the cost of the heater and complicate the manufacturing process. These high speed, low current fans include many windings of small gauge wire which is prone to breakage and is more expensive relative to heavier gauge magnetic motor wire. As such, these motors represent a major cost component of the heater.
Various improvements have been proposed with respect to portable heaters to include additional features such as night lights or combining these heaters with other appliances such as humidifiers.
The purchase of a portable heater remains a price sensitive purchase as the heater is typically solving a specific problem requiring a temporary solution. Therefore, effective design of the portable heater is required to produce an acceptable product.